In a recent preprint 1302.1929 my co-authors and I make use of some results about the character theory of extraspecial groups. These were largely gleaned from haphazard Googling, comments made by people on MO, and playing around by ourselves.

Because the paper is probably going to be read by people in Banach algebras/harmonic analysis rather than by finite group theorists, the referee has requested that we provide references for the following assertions: if $G$ is a group with prime power order where the centre and derived subgroup coincide and have order $p$, for $p$ a prime, then each non-linear irreducible character has degree $p^n$ where $|G|=p^{2n+1}$, and is supported on $Z(G)$.

Now while this does not look hard to prove directly, just using fairly basic character theory, I would like to know if this is written down *explicitly* somewhere where I can cite it. The Wikipedia page for extraspecial groups lists Gorenstein's book on finite groups as a reference, but my library doesn't have a copy.

Can anyone suggest a suitable reference? (I would like to check that no such convenient reference exists before writing out a proof in the paper.)